Development of a 100 watt S-band traveling- wave tube Quarterly progress report

Development of 100 watt S band traveling wave tube for space application

Factors Influencing Variation in Susceptibility of Prairie Plants to an Early Summer Frost in East-Central Minnesota

This study was conducted to determine the factors affecting susceptibility of prairie plants to an early summer frost at Cedar Creek Natural History Area, in east-central Minnesota. Data were collected in a previously established experimental field after temperatures fell to 1.3 °C on 20 June 1992, and to 0.3 °c on 21 June 1992. The degree of frost damage to prairie plants was recorded using a scale of frost damage based on visual criteria, and possible causes of variation in frost susceptibility were examined. The degree of frost damage was independent of plant type (grass or forb), life cycle (annual, perennial, or biennial), successional status (early or late), and species origin (native or introduced). No significant correlations were noted between plant height and mean frost damage but there was a significant negative correlation between plant height and maximum frost damage. In addition, there were no significant correlations between frost damage and mean plant biomass allocated to leaves, stems, and roots, mean biomass allocations aboveground and below-ground, and total biomass. However, plants that allocated a greater proportion of biomass to leaves were more severely damaged than plants which allocated less biomass to leaves. The ratio of leaves to total biomass appears to be critical in relation to frosting events because leaves have a high surface area to volume ratio, which allows more surface area to be exposed to cold air masses, thus increasing the freezing rate

Microwave intermodulation distortion of MgB2 thin films

The two tone intermodulation arising in MgB2 thin films deposited in-situ by planar magnetron sputtering on sapphire substrates is studied. Samples are characterised using an open-ended dielectric puck resonator operating at 8.8 GHz. The experimental results show that the third order products increase with the two-tone input power with a slope ranging between 1.5 and 2.3. The behaviour can be understood introducing a mechanism of vortex penetration in grain boundaries as the most plausible source of non linearities in these films. This assumption is confirmed by the analysis of the field dependence of the surface resistance, that show a linear behaviour at all temperatures under test.Comment: 13 pages, 3 figures; to be published in Appl. Phys. Let

Large Area Crop Inventory Experiment (LACIE). User requirements

There are no author-identified significant results in this report

Zhx2 (Zinc Fingers and Homeoboxes 2) Regulates Major Urinary Protein Gene Expression in the Mouse Liver

The mouse major urinary proteins (Mups) are encoded by a large family of highly related genes clustered on chromosome 4. Mups, synthesized primarily and abundantly in the liver and secreted through the kidneys, exhibit male-biased expression. Mups bind a variety of volatile ligands; these ligands, and Mup proteins themselves, influence numerous behavioral traits. Although urinary Mup protein levels vary between inbred mouse strains, this difference is most pronounced in BALB/cJ mice, which have dramatically low urinary Mup levels; this BALB/cJ trait had been mapped to a locus on chromosome 15. We previously identified Zhx2 (zinc fingers and homeoboxes 2) as a regulator of numerous liver-enriched genes. Zhx2 is located on chromosome 15, and a natural hypomorphic mutation in the BALB/cJ Zhx2 allele dramatically reduces Zhx2 expression. Based on these data, we hypothesized that reduced Zhx2 levels are responsible for lower Mup expression in BALB/cJ mice. Using both transgenic and knock-out mice along with in vitro assays, our data show that Zhx2 binds Mup promoters and is required for high levels of Mup expression in the adult liver. In contrast to previously identified Zhx2 targets that appear to be repressed by Zhx2, Mup genes are positively regulated by Zhx2. These data identify Zhx2 as a novel regulator of Mup expression and indicate that Zhx2 activates as well as represses expression of target genes

Enhanced ionization in small rare gas clusters

A detailed theoretical investigation of rare gas atom clusters under intense short laser pulses reveals that the mechanism of energy absorption is akin to {\it enhanced ionization} first discovered for diatomic molecules. The phenomenon is robust under changes of the atomic element (neon, argon, krypton, xenon), the number of atoms in the cluster (16 to 30 atoms have been studied) and the fluency of the laser pulse. In contrast to molecules it does not dissappear for circular polarization. We develop an analytical model relating the pulse length for maximum ionization to characteristic parameters of the cluster

Insulin resistance in type 1 diabetes: what is ‘double diabetes’ and what are the risks?

In this review, we explore the concept of ‘double diabetes’, a combination of type 1 diabetes with features of insulin resistance and type 2 diabetes. After considering whether double diabetes is a useful concept, we discuss potential mechanisms of increased insulin resistance in type 1 diabetes before examining the extent to which double diabetes might increase the risk of cardiovascular disease (CVD). We then go on to consider the proposal that weight gain from intensive insulin regimens may be associated with increased CV risk factors in some patients with type 1 diabetes, and explore the complex relationships between weight gain, insulin resistance, glycaemic control and CV outcome. Important comparisons and contrasts between type 1 diabetes and type 2 diabetes are highlighted in terms of hepatic fat, fat partitioning and lipid profile, and how these may differ between type 1 diabetic patients with and without double diabetes. In so doing, we hope this work will stimulate much-needed research in this area and an improvement in clinical practice